Recently, a small-sized and high-capacitance capacitor used for high frequency applications has been desired along with downsizing and lightening of electronic devices. As such a capacitor, a solid electrolytic capacitor having low equivalent series resistance (ESR) and excellent frequency characteristics has been developed. The solid electrolytic capacitor includes an anode body, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer formed on a surface of the dielectric layer. As the anode body, there can be used a porous sintered body obtained by sintering particles of a valve metal such as tantalum, niobium, or titanium.
The porous sintered body is usually produced by subjecting valve metal particles to pressing, followed by sintering. In the production, when a density of valve metal particles is too increased in the sintered body, an impregnation property of the sintered body deteriorates with respect to a raw material liquid for forming a solid electrolyte layer. Therefore, it becomes sometimes difficult to form a sufficient solid electrolyte layer on the surface of the dielectric layer.
In order to solve such a problem, Unexamined Japanese Patent Publication No. 2010-165701 discloses an anode body including a first sintered body having low density and a second sintered body having higher density than the first sintered body is used, the second sintered body disposing around the first sintered body. Further, in Unexamined Japanese Patent Publication No. 2010-153625, a sintered body is sandwiched between higher-density sintered bodies to improve bending strength and strength at a corner of an anode body.